One example of such a device is an ACC (Adaptive Cruise Control) system which makes it possible to adjust the velocity of a vehicle to the velocity of a preceding vehicle, located with the help of a radar system, so that the preceding vehicle is followed at a suitable safety distance. To do so, the driver assistance system intervenes in the drive system and, if necessary, also intervenes in the brake system of the vehicle. The intervention in the brake system has conventionally been accomplished by regulating the braking deceleration to a setpoint braking deceleration calculated by the driver assistance system. When this regulation takes place in the brake control unit, the setpoint braking deceleration forms the brake request signal which is output by the driver assistance system.
ACC systems in use today are generally designed for travel at a high velocity, e.g., on a highway. However, there are efforts to expand the function range of such systems to low velocities and in particular to include a stop-and-go function in which the vehicle is automatically brakable to a standstill when the preceding vehicle stops, e.g., in a traffic jam. The problem occurring then is that inaccuracies during measuring of the actual braking deceleration have serious effects at low velocities, so that regulation becomes unstable. The non-steady transition to a standstill (stopping jolt) is a particular problem here. In vehicles having an automatic transmission, the brake must also be operated at a standstill to prevent the vehicle from rolling. However, since the actual braking deceleration is equal to zero at a standstill, the brake request signal cannot be defined at a standstill via a setpoint braking deceleration.
These problems are avoidable or at least alleviatable if the brake request signal output by the driver assistance system is not represented by a setpoint braking deceleration but instead directly by a brake pressure signal. However, since the deceleration of the vehicle achieved with a given brake pressure depends on the particular vehicle model and the condition of the brakes (temperature, moisture), in this case the driver assistance system must be adjusted to the particular vehicle model and must also be able to process a plurality of parameters related to the condition of the brake system.